激发相干态光场与级联型三能级原子相互作用的场熵与场的线性熵演化特性

本文研究了激发相干态光场与级联型三能级原子相互作用过程中场熵及场的线性熵的演化规律,结果表明：场熵和场的线性熵随时间的演化规律基本相同,二者均具有明显的振荡特性,随着光场参数α值或m值的不断增大,场熵和场的线性熵的演化均呈现量子崩塌和复苏现象,且它们随α值增大的变化比随m值增大的变化要快得多,即场熵和场的线性熵更敏感于α值的变化。     

Some detection and resolution properties of maximum entropy spectrum analysis

An experimental comparison between conventional spectral estimation techniques and a Maximum Entropy Spectral Analysis (MESA) algorithm is made. Three factors in the experimentation make the results of considerable interest to workers in acoustic signal processing, especially sonar and surveillance. These are the range of signal-to-noise ratio (SNR) studied, the comparisons based equal length observation intervals and the use of ensemble averaging after maximum entropy analysis. Results are presented, for both resolution and peak signal response, which tend to indicate that the Maximum Entropy Method (MEM) offers considerable promise in achieving the detection performance of long observation interval discrete Fourier transform (DFT) analysis at a much reduced length of observation time.     

First-principles study on electronic properties and lattice structures of WZ-ZnO/CdS interface

We theoretically investigated the lattice structure, interface bonding energy, optical absorption properties and electronic properties of WZ-ZnO (1 1 2)/CdS (1 1 0) interface from first-principles calculations. The interface lattice mismatch is less than 4.3%. The atomic bond lengths and atomic positions change slightly on the interface after relaxation. The WZ-ZnO (1 1 2)/CdS (1 1 0) interface has bonding energy about −0.61 J/m², suggesting that this interface can exist stably. Through analysis of the density of states, no interface state is found near the Fermi level. In addition, there are orbital hybridizations between different interfacial atoms, and these orbital hybridizations effectively enhance the bonding of Zn and S atoms, Cd and O atoms on the interface. By analysis of difference density charge and Bader charge, we find that electrons on the interface are largely redistributed and charges transport near the Fermi level which strengthen the adhesion of the interface.     

Ray propagation in a random lattice: a maximum entropy, anomalous diffusion Process

The typical model for diffusion in disordered systems is that of a random walk that proceeds in discrete steps over a random lattice, where not all the nearest sites can be reached at each step. We study the related problem of ray propagation in percolating lattices, and observe that it follows an anomalous diffusion process, whose appropriate metric is the "Manhattan" distance defined by the lattice geometry. The proposed solution is the one that exhibits the maximum Shannon's entropy, among all propagation processes with appropriate moment constraints imposed by the geometry of the lattice. Ray propagation in percolating lattices has been recently proposed as a model for urban area propagation of radio waves. We discuss implications of our results in this scenario.     

克尔媒质中耦合三能级T-C模型中原子信息熵的性质

利用全量子理论,讨论了克尔媒质中耦合V型三能级原子与相干态光场相互作用过程中原子信息熵的演化特性。数值计算结果表明,原子信息熵的演化特性对系统初始时刻场平均光子数的大小很敏感。初始时刻场的平均光子数比较大时,原子信息熵的演化会出现明显的周期性崩塌和回复现象。初态中原子激发态概率幅、原子间耦合强度、失谐量与克尔系数等系统...     

Bounds on the entropy series

Upper bounds on the entropy of a countable integer-valued random variable are furnished in terms of the expectation of the logarithm function. In particular, an upper bound is derived that is sharper than that of P. Elias (ibid., vol.IT-21, no.2, p.194-203, 1975), for all values of E_p(log). Bounds that are better only for large values of E_p than the previous known upper bounds are also provided     

On the resolution properties of an adaptive algorithm for maximum entropy spectrum analysis

The resolution properties of the adaptive mean squares algorithm when used for maximum entropy spectrum estimation are compared with those of Burg's algorithm and the standard periodogram method using the FFT algorithm.     

正方晶格光子晶体第一带隙特性研究

由于光子晶体的禁带特性具有重要的应用,基于电磁波传输理论,应用MATLAB数值仿真二维正方晶格光子晶体TE模第一带隙特性,数值计算了介电常数变化、填充率变化对第一带隙宽度及形成带隙个数的影响,结果得到随着介电常数的增加第一带隙宽度增加,随着填充率的增加,第一带隙宽度逐渐减小。研究结论为光子晶体器件的制作提供参考。     

The effect of neutron irradiation and annealing temperature on the electrical properties and lattice constant of epitaxial gallium nitride layers

Effect of irradiation with high reactor-neutron fluences (Φ = 1.5 × 10¹⁷-8 × 10¹⁹ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and lattice constant of epitaxial GaN layers grown on an Al₂O₃ substrate is considered. It is shown that, with the neutron fluence increasing to (1–2) × 10¹⁸ cm⁻², the resistivity of the material grows to values of about 10¹⁰ Ω cm because of the formation of radiation defects, and, with the fluence raised further, the resistivity passes through a maximum and then decreases to 2 × 10⁶ Ω cm at 300 K, which is accounted for by the appearance of a hopping conductivity via deep defects in the overlapping outer parts of disordered regions. With the neutron fluence raised to 8 × 10¹⁹ cm⁻², the lattice constant c increases by 0.38% at a nearly unchanged parameter a. Heat treatment of irradiated samples at temperatures as high as 1000°C does not fully restore the lattice constant and the electrical parameters of the material.     

A note on the absolute epsilon entropy

A novel characterization of the absolute epsilon entropy of an ergodic information source is presented. This characterization allows one to derive a new lower bound to this quantity, which is shown to be tight in some interesting special cases     

Comments on the performance of maximum entropy algorithms

Two points recently brought up in this journal concerning the performance of maximum entropy spectral analysis are discussed. First, an additional recursive formula is presented which simplifies and reduces the computational load of the Burg algorithm. Second, attention is drawn to some recent results in the geophysics literature related to the proper selection of prediction filter length.     

Divergence measures based on the Shannon entropy

A novel class of information-theoretic divergence measures based on the Shannon entropy is introduced. Unlike the well-known Kullback divergences, the new measures do not require the condition of absolute continuity to be satisfied by the probability distributions involved. More importantly, their close relationship with the variational distance and the probability of misclassification error are established in terms of bounds. These bounds are crucial in many applications of divergence measures. The measures are also well characterized by the properties of nonnegativity, finiteness, semiboundedness, and boundedness     

Survey and comparative analysis of entropy and relative entropy thresholding techniques

Entropy-based image thresholding has received considerable interest in recent years. Two types of entropy are generally used as thresholding criteria: Shannon's entropy and relative entropy, also known as Kullback-Leibler information distance, where the former measures uncertainty in an information source with an optimal threshold obtained by maximising Shannon's entropy, whereas the latter measures the information discrepancy between two different sources with an optimal threshold obtained by minimising relative entropy. Many thresholding methods have been developed for both criteria and reported in the literature. These two entropy-based thresholding criteria have been investigated and the relationship among entropy and relative entropy thresholding methods has been explored. In particular, a survey and comparative analysis is conducted among several widely used methods that include Pun and Kapur's maximum entropy, Kittler and Illingworth's minimum error thresholding, Pal and Pal's entropy thresholding and Chang et al.'s relative entropy thresholding methods. In order to objectively assess these methods, two measures, uniformity and shape, are used for performance evaluation     

光环晶格的产生与传输研究

理论和实验研究了单环与多环晶格的产生及空间传输特性。数值结果表明,光环晶格初始产生时共轴叠加的拉盖尔高斯涡旋光束拓扑荷之差决定着光强分布中亮暗花瓣状光斑数量;暗环晶格的相位分布存在奇异点,与光强分布中暗花瓣状光斑数量及位置相互对应,亮环晶格相位分布中无奇异点;随传播距离的增加,光环晶格的亮暗花瓣状光斑均远离光束中心,暗环晶格拓扑荷为正值发生顺时针旋转,为负值则发生逆时针旋转,亮环晶格无旋转特性。实验上,利用反射式空间光调制器产生了光环晶格并使用CCD记录保存,探究了光环晶格的光强分布以及空间传输特性。实验结果与理论结果基本符合,该研究成果为光环晶格的冷原子捕获提供了一定的理论与实验依据。     

Some asymptotic properties of the entropy of a stationary ergodicdata source with applications to data compression

Theorems concerning the entropy of a stationary ergodic information source are derived and used to obtain insight into the workings of certain data-compression coding schemes, in particular the Lempel-Siv data compression algorithm     

椭圆孔六角点阵聚合物光子晶体光纤的偏振特性研究

基于全矢量平面波方法,以聚甲基丙烯酸甲酯为基材,设计了一种高双折射光子晶体光纤,并对其传输性质和偏振特性进行了数值模拟。结果表明,椭圆孔六角点阵聚合物光子晶体光纤的双折射是由于包层的不对称性引起的全局双折射,通过调节椭圆率,发现该光纤可以以单模方式在一合适波段运行,该波段与聚合物光纤的低损耗通信窗口一致。并且在 时,其双折射最高可达 。该研究结果为高双折射聚合物光子晶体保偏光纤的制备提供了理论依据。     

有中心缺陷孔的矩形点阵PCF双折射特性研究

采用全矢量有限元法研究了具有中心椭圆缺陷孔的矩形点阵PCF(光子晶体光纤)的双折射特性。结果发现,该新型PCF的双折射特性对波长和光纤的结构参数具有较强的依赖关系,与无中心椭圆缺陷孔的矩形点阵PCF相比,在中心缺陷孔参数bc/Λ=0.075、中心空气孔椭圆率η=2.2、包层结构参数Λ=2.0μm和d/Λ=0.48时,该新型PCF具有更高的双折射。     

基于信息熵和Gabor滤波器的图像检索

采用颜色和纹理的多特征提取,将图像按照一定的规则进行分块,对各个分块分别进行各种特征向量的提取.采用HSV颜色空间把颜色特征量化到72个颜色空间得到72柄的一维直方图,计算图像信息熵;纹理特征采用Gabor滤波器.该种分块方法能够很好的利用图像内容的空间信息,综合颜色和纹理特征能够有效地提高查全率和差准率.     

Guesswork and entropy

We derive the moments of the guesswork , the number of attempts required to correctly guess the output of a random source, for a source determined by a Markov chain via a large deviations type estimate. These moments are related to the Perron-Frobenius eigenvalue of the matrix formed by element-wise powers of the Markov chain's transition matrix.